Electric furnace and tubular heating element for use therewith



Aug. 25, 1970 w WESTEREN ET AL 3,525,795

ELECTRIC FURNACE AND TUBULAR HEATING ELEMENT FOR USE THEREWITH FiledApril 29,,1968 2 Sheets-Sheet 1 INVENTORS HERBERT W. WESTEREN WILLIAM H.KIMBALL ,fwm $1M ATTORNEYS ELECTRIC FURNACE AND TUBULAR HEATING ELEMENTFOR USE THEREWITH Filed April 29 1968 5, 1970 H. w. WESTEREN ET AL 2Sheets-$heet 2 INVENTORS HERBERT W. WESTEREN WILLIAM H. KIMBALLATTORNEYS United States Patent O US. CI. 13-25 Claims ABSTRACT OF THEDISCLOSURE An electric furnace having a heating chamber in which aheating element is located, the resistance heating element beingcomprised of a flexible graphite cloth material that has a generallytubular configuration.

BACKGROUND OF THE INVENTION Electric furnaces known heretofore used inthe heat treatment of metallic articles have usually incorporatedmetallic or ceramic type resistance heating elements in the heatingchambers thereof. Although these prior known heating elements were foundto be satisfactory for many purposes, they had a tendency to expandunevenly and were therefore somewhat brittle after a period of use.Moreover, the prior known resistance heating element was relativelyexpensive to operate and required a special terminal construction in theuse thereof.

Prior to the instant invention, resistance heating elements formed of aflexible graphite material have. been employed in an electric furnaceconstruction as a substitute for the metallic resistance heating elementand have been found to be efficient in operation and relativelyinexpensive in the fabrication and use thereof. The use of such flexiblecloth graphite heating elements is illustrated and described in Pat. No.3,257,492. Although the graphite cloth heating element as employed inthe heating chamber of a furnace construction and described in theaforesaid patent has been found to be efficient in operation and isrelatively inexpensive in the use thereof, the manner of applicationthereof was still limited when incorporated in certain types of highvacuum electric furnaces. It is desirable in vacuum furnaces to limitthe number of feed-throughs in the furnace wall, and when it wasnecessary to increase the temperature requirements in the heatingchamber using the prior known graphite heating elements additionalterminals were required necessitating additional, special insulatedpower feed-through in the furnace walls. Such special feed-throughs,that were required to penetrate through a double-wall vacuum vessel,constituted an item of considerable expense.

SUMMARY OF THE INVENTION The present invention relates to an electricfurnace that incorporates a graphite heating element in the heatingchamber thereof, and although the invention is not limited to anelectric furnace of the vacuum type, it has particular applicationtherewith. Because the furnace as conteinplated for use herewith doesoperate under vacuum, it is desirable to reduce the number of fittingsextending through the walls thereof, and in this connection the heatingelements as employed in the present invention are connected to spacedterminal bars that extend through the furnace walls, and thus, not onlyare the number of fittings that extend through the furnace wallsreduced, but a concentrated heating area is defined by the arrangementof the heating elements. In the present invention, the heating elementas used in the furnace heating chamber is constructed of a flexiblegraphite cloth material in a tubu: lar configuration and is mounted inplace by fitting the 3,525,795 Patented Aug. 25, 1970 ends thereof overcylindrical portions of rigid graphite terminals. A compression ringenvelopes the cloth on the cylindrical portion of the terminal andcooperates therewith to lock the end of the cloth in place. Preferably,the cylindrical portion and the compression ring have a correspondingtapered configuration that provides for maintaining a tight fit as thecloth is captured therebetween. By locating the heating elements betweenspaced terminal bars in a relatively unflexed position a relativelyconfined heating area is defined.

Each of the terminals to which a heating element is secured is formedwith an elongated portion, these portions being interconnected to theterminal bars that extend through the walls of the vacuum vessel. Thus,the spaced terminal bars have a plurality of the terminalsinterconnected thereto and act to locate any number of graphite tubularheating elements in parallel spaced relation within the furnace heatingchamber. However, regardless of the number of heating elements that arelocated in the heating chamber, only a limited number of feedthroughsextend through the furnace walls.

Accordingly, it is an object of the present invention to provide anelectric furnace having a flexible heating element for use therewith.

Another object of the invention is to provide a vacuum electric furnacein which a plurality of heating elements having a tubular configurationand formed of a flexible graphite cloth material are located in thefurnace heating chamber and are interconnected to terminal bars inspaced parallel relation.

Still another object is to provide a flexible heating element for use inan electric furnace that is formed in a tubular configuration and thatis secured to a terminal bar at the end thereof by means of aninterfitting compression ring and cylindrical portion.

Other objects, features and advantages of the invention will becomeapparent as the description thereof proceeds when considered inconnection with the accompanying illustrative drawings.

DESCRIPTION OF THE DRAWINGS In the drawings which illustrate the bestmode presently contemplated for carrying out the present invention:

FIG. 1 is a horizontal sectional view through the heating chamber of anelectric furnace showing in top plan a plurality of heating elements ofthe present invention that are located in spaced parallel relation andare connected to spaced terminal bars;

FIG. 2 is an elevational view showing a heating element of the presentinvention as attached to end terminals;

FIG. 3 is an enlarged view of a portion of a terminal bar showing aconnection for receiving one of the terminals that is interconnected tothe heating element;

FIG. 4 is an enlarged view with parts shown in section of a portion of aterminal bar illustrating another connection for receiving the otherterminal that is inter.- connected to the heating element;

FIG. 5 is an enlarged view of a terminal with parts shown in section andillustrating the interconnection of a tubular heating element therewith;

FIG. 6 is a sectional view taken along lines 66 in FIG. 5; and

FIG. 7 is an exploded perspective view of a portion of a tubular heatingelement and the associated terminal.

DESCRIPTION OF THE INVENTION Referring now to the drawings andparticularly to FIG. 1, a high-vacuum heat treatment furnace of thecold-wall type is illustrated and is generally indicated at 10. Thefurnace 10 as illustrated in FIG. 1 is broken away so that only theheating chamber indicated at 11 is shown. The remaining portions of thefurnace, including the loading end, the cooling station and a quencharea, are not illustrated herein and form no part of the presentinvention.

Mounted on opposed brackets 12 and 14 is the furnace housing theinterior wall of which is indicated at 16. Spaced from the interior wall16 is an outer wall 18 that cooperates therewith to define a coolingchamber 18 in which a cooling fluid, such as water, is circulated. Notshown are connections that extend through the walls 16 and 18 and thatcommunicate with a vacuum pump, the vacuum pump being adapted toexacuate the interior of the furnace to a predetermined vacuum forcarrying out the heat treatment operation.

Located in the heating chamber 11 of the furnace is an arrangement oflaminated graphite insulating sections indicated at 20, 22, 24 and 26and that cooperate to form a confined heating area therebetween. Asfurther illustrated in FIG. 1, a carriage 28 is provided and is movableon tracks (not shown) for transferring a workload between a load and/ orcooling station and the heating chamber 11. The construction of thecarriage 28 and the means for carrying out the movement thereof do notform any part of the present invention.

In order to supply the required heat for the heating area, opposed powerfeed-throughs indicated at 30 and 32 are provided and extend through thehousing walls 16 and 18 for communication with a source of current.Spaced tubular bus or terminal bars 34 and 36 extend laterally acrossthe heating chamber 11 exteriorly of the insulating sections and areelectrically interconnected to the power feed-throughs 30 and 32,respectively. Joined to the tubular terminal bar 34 are a plurality ofinteriorly threaded sleeve connectors 38, while joined to the tubularterminal bar 36 are a plurality of slotted sleeve connectors 40. Asshown in FIG. 1 each of the sleeve connectors 38 is aligned with asleeve connector 40 and, as will be described hereinafter, each alignedpair of connectors are adapted to mount a heating element indicated at42 therebetween. Water is normally circulated through the tubularterminal bars 34 and 36 for maintaining them at an operatingtemperature, and it is seen that since all of the heating elements 42are interconnected to the terminal bars 34 and 36, only fourfeed-throughs as indicated at 30 and 32 are required for extendingthrough the walls of the furnace housing. Thus it is seen that a numberof the heating elements 44 may be concentrated in the heating area toform a confined heating zone, wherein the required temperature may beobtained in the heating area Within a minimum period of time and may bemaintained thereat with little temperature variation.

As shown in FIG. 3, each of the sleeve connectors 40 is welded to theterminal bar 36 and is slotted as indicated at 44 to form aflexible-type connection. A compression clamp 46 is mounted on eachconnector 40 and, as will be described, is adapted to clamp a firstheating element terminal therein. The connector element 38, on the otherhand, is interiorly threaded, as indicated at 48 and is also welded toits associated terminal bar 34. A second terminal that is joined to theheating element 42 is received in threaded relation in the connector 38and cooperates with the first terminal for securing the heating element42 between the terminal bars 34 and 36.

Referring now to FIGS. 2, 5, 6 and 7, one of the heating elements 42 isshown in detail and, as illustrated, is formed of a flexible graphitecloth material that is woven and as constructed in accordance with thepresent invention is arranged in a tubular configuration. The tubulargraphite heating element 50 may be woven in the tubular form, or it maybe woven in a web, cut and then wrapped in the tubular configuration.With respect to the use of the graphite cloth material as a heatingelement in web form, reference is made to Pat. No. 3,257,492. In thepresent invention, as illustrated in FIGS. 5, 6 and 7, the tubulargraphite cloth 50 is supported at the ends thereof by terminalsgenerally indicated at 52 and 54. As will be described, the terminals 52and 54 are similarly constructed, except that the outer ends thereof areespecially formed for being secured to their respective terminal bars 34and 36. Referring again to FIGS. 5 and 7, the terminal 52 is shownincluding a cylindrical portion 56 on which spaced annular lands 58 and'60 are formed. The lands 58 and 60 define a groove 62 therebetween,and, as illustrated in FIG. 5, the peripheral surface of the cylindricalportion 56 as defined by the lands 58 and 60 has a taper that decreasesin a direction away from the land 60 and toward the land 58. Integrallyjoined to the cylindrical portion 56 is a bar portion 64, the outer endof which is threaded as indicated at 66. The threaded end 66 of the barportion 64 is receivable in threaded relation in the threaded portion 48of a connector 38, thereby securing the terminal 52 to the terminal bar34. In order to fix the tubular heating element 50 to the terminal 52, acompression or retaining ring 68 is provided, and has an inner taperedsurface that conforms to the taper of the lands 58 and 60. The diameterof the lands 58 and 60 is dimensioned to receive the tubular cloth 50therearound and with the cloth mounted on the cylindrical portion 56 asillustrated in FIG. 5, the ring 68 is forced thereover so as to capturethe end of the cloth 50 therebetween and the cylindrical portion 56. Byforming the lands 58 and 60 with the groove 62 therebetween, pointcontact is provided between the lands and the inner surface of the ring68, wherein the end of the cloth 50 is firmly locked on the cylindricalportion 56 of the terminal 52.

The terminal 54 is constructed substantially identical to the terminal52, except that the outer end thereof is smooth, as indicated at 70,rather than being threaded as previously described. The smooth end 70 ofthe terminal 54 is received within a connector 40 that is joined to theterminal bar 36, and the compression clamp 46 is then clamped around thesleeve connector 40 by tightening a screw 72, thereby securely lockingthe terminal 54 within the connector 40.

In the assembly of the graphite heating elements 42 between the terminalbars 34 and 35, the ends of the heating elements are first locked inplace on the cylindrical portions of the terminals by the retainingrings 68. Each terminal 52 is then threadably secured to a connector 38on the terminal bar 34. The heating elements 42 are then stretched totheir full length so as to be substantially unfiexed, and the smoothportions 70 formed on the bar portions 64 of the terminals 54 areinserted within the connectors 40 and clamped in place therein by thecompression clamp 46. The heating elements 42 are thus mounted betweenthe terminal bars 34 and 36 in spaced parallel relation in the heatingchamber 11 of the furnace.

The plurality of tubular heating elements 42 as located in the heatingchamber area of the furnace provide a concentrated plane of heat withina relatively confined area. Since the heating elements are joined to theopposed terminal bars 34 and 36, only a limited number of throughconnections are required for insertion through the furnace walls. Themanner of connecting the heating elements 42 to the terminal bars issimple and can be accomplished with a minimum of effort and since theretaining rings 68 define a friction fit around the tubular clothelements 42 the whole assembly may be dismantled with relative ease. Theuse of the tapered fit between the compression ring 68 and thecylindrical portion 56 of the terminal insures a tight fit and a goodelectrical connection between the graphite cloth tubes and theterminals. All of the heating elements and terminals are standardized;and with the exception of the threaded end of one terminal and thesmooth end of the other terminal, the parts can be interchanged. Thevarious arrangements of the tubular elements and the variations in thematerial resistance as defined by the woven graphite cloth offerconsiderable design flexibility, and the physical configuration of thetubular heating elements is such that high velocity cooling can becarried out in the heating chamber with minimum element attrition.

While there is shown and described herein certain specific structureembodying the invention, it will be manifest to those skilled in the artthat various modifications and rearrangements of the parts may be madewithout departing from the spirit and scope of the underlying inventiveconcept and that the same is not limited to the particular forms hereinshown and-described except insofar as indicated by the scope of theappended claims.

What is claimed is:

11. An electric furnace comprising a housing having a heating chamberlocated therein, a resistance heating element assembly mounted in saidheating chamber and including at least one elongated resistance heatingelement formed of a flexible, graphite cloth material and having agenerally tubular configuration, and terminals located at the ends ofsaid tubular heating element and being connected thereto for electricalcommunication therewith, said terminals being formed of a solid graphitematerial that has electrical conducting characteristics, the terminalslocated at the ends of said tubular heating element including acylindrical portion to which an elongated portion is integrally joined,said cylindrical portion of each terminal being received within an endand the elongated portion projecting outwardly thereof, for junctionwith a source of current, and a securing ring interfitting over thetubular element on the cylindrical portion of the terminal, wherein saidtubular heating element is captured between said cylindrical portion andsecuring ring.

2. An electric furnace as set forth in claim 1, said cylindrical portionhaving an annular groove formed therein that defines annular lands, saidring capturing said tubular resistance heating elements therebetween andsaid lands wherein said lands provide for secure engagement of said ringtherewith.

3. An electric furnace as set forth in claim 2, the peripheral surfaceof said lands having an increasing taper toward said elongated portion,and the inner surface of said ring having a corresponding taper, whereinthe interfitting tapered lands and tapered ring efiectively capture thetubular element therebetween and provide for a firm mounting of saidelement on the associated terminal.

4. 'An electric furnace as set forth in claim 1, the elongated portionof one of said terminals having a threaded end, the elongated portion ofthe other terminal having a nonthreaded end, said source of currentincluding spaced terminal bars, one of which has a threaded sleevejoined thereto for threadably receiving the threaded end of said oneterminal, and the other of said terminal bars having a nonthreadedsleeve for clampingly receiving the nonthreaded end of the otherterminal.

5. An electric furnace as set forth in claim 4, each of said spacedterminal bars having a plurality of sleeves joined thereto that arelocated in aligned relation with sleeves joined to the opposed terminal,and a plurality of the flexible tubular resistance heating elementsfixed between said terminal bars in spaced, parallel relation.

6. A resistance heating element for use in an electric furnace,comprising a body portion formed of a flexible, graphite cloth materialand having a tubular configuration, and electrical terminals mounted inspaced relation at the ends of said body portion and secured thereto formounting said tubular body portion in a relatively unflexed positiontherebetween.

7. A resistance heating element as set forth in claim 6, each of saidterminals including a cylindrical portion to which a longitudinalportion is joined, an end of the body portion of said heating elementbeing received over the cylindrical portion, and a securing ringinterfitting over said cylindrical portion for capturing the tubularbody portion therebetween.

8. A resistance heating element as set forth in claim 7, the peripheralsurface of said cylindrical portion being tapered and the inside surfaceof said ring having a corresponding taper, wherein the tubular bodyportion is tightly interlocked between said cylindrical portion and ringwhen they are interfitted With the tubular body portion capturedtherebetween.

9. An electric furnace comprising a housing having a heating chamberlocated therein, a resistance heating element assembly mounted in saidheating chamber and including at least one elongated resistance heatingelement having a body portion formed of a flexible, woven graphite clothmaterial and having a generally tubular configuration, and terminalslocated at the ends of said tubular heating element and being connectedthereto for electrical communication therewith, each of said terminalshaving a cylindrical portion that receives an end of said tubularheating element and that communicates with a source of current, andclamping means coop crating with the cylindrical portion of eachterminal for securing an end of the body portion of each heating elementthereon.

10. A resistance heating element for use in an electric furnace,comprising a body portion formed of a flexible, graphite cloth materialand having a tubular configuration, and terminals located in spacedrelation at the ends of said body portion and secured thereto formounting said tubular body portion in a relatively unfiexed positiontherebetween, each of said terminals including a cylindrical portionthat receives an end of the body portion of said heating element, andclamping means cooperating with the cylindrical portion of each terminalfor securing an end of the body portion of said heating element thereon.

References Cited UNITED STATES PATENTS 3,120,597 2/1964 Maloof et al.1325 X 3,178,665 4/1965 Matheson et al. 1325 X 3,400,253 9/1968 Marker219531 X 3,361,863 l/1968 Lang 219-541 X 3,236,205 2/1966 Kopito 219-531X H. B. GILSON, Primary Examiner US. Cl. X.R. 219531, 541

